He talks about holding midfielders and defensive midfielders all the time in the book, I don't know why anyone would think it goes against the idea of him having a defensive midfielder. Lahm going there was the biggest decision of the season, then he decided he needed 2 holding midfielders not 1, he was converting Javi Martinez from holding midfielder to centre back etc.
"He's the best defensive central midfielder in the world." - Guardiola on Busquets playing pretty much the role of our guy at the base of midfield.
‘He is one of the best holding midfielders I’ve ever seen in my life by far. He’s the level of Xabi Alonso and Sergio Busquets.’ - Being generous with the praise for Carrick.
I don't know where this semantic debate has arisen from over the last few days that Pep either a) doesn't want/use a defensive midfielder or b)Jorginho isn't a defensive midfielder but it's all a load of shite, seemingly coming about because people can't work out that a 6'3'' clogger in the middle of the park isn't the only type of defensive mid.
Jorginho is a holding midfielder, Fernandinho is a holding midfielder. Both have different strenghts and weakness, sometimes both might play, otherwise it'll be horses for courses.
As for the point you bring up with headers - you're right that Fern has become our main defender of aerial balls, with the CB's mopping up the knock downs, or picking up the runners rather than challenging the target man themselves which is what was happening before that Leicester City game when they murdered us getting the second ball every time. With Jorginho that might have to be reversed, putting someone like Laporte on the big man, and having Jorginho mop up and the other CB track any runners.
What will be interesting to me is if that change is made permanently or just when Jorginho is playing. I don't like the idea of CB's having to switch half way through a match or from game to game because I can already see Stones/Otamendi not realising they were supposed to track the runner this time and some relegation candidate team scores against us when someone is 1v1 from a flicked on header.